Synthesis And Photoelectric Properties Of CdS Nanorod Arrays And Its Heterogeneous Structures

The utilization of the solar energy is a hot and permanent subject. Exploiting photoelectric functional materials with top performance is the foundation for solar energy conversion. As a typicalⅡ-Ⅵsemiconductor, CdS attracts many attentions for its high extinction coefficient in visible spectrum and large intrinsic dipole moment that leads to rapid charge separation. In recent years, many efforts have been focused on the modification of CdS nanostructures by introducing a second semiconductor compound to form heterostructures. It is cognized that the heterogeneous structure can hold up photo corrosion and improve the photoelectric properties of functional materials based on cadmium sulphide. However, few report expounds the behaviors of photogenerated charges (the generation, separation, transportation and recombination) of CdS nanostructrues and its heterostructures. While, this is the basic for developing the advanced materials with photo-to-electric converting function.In this paper, We fabricated large-scale CdS nanorod arrays with different morphologies by hydrothermal approach. And then CdS/ZnO, CdS/ZnS heterostructures was design on that basis. We studied the photoelectric properties of the above systems by surface photovoltage (SPV) technique and the transient photovoltage (TPV) technique and obtained some novel results.1. Well-defined hexangularly faced CdS nanorod arrays with different length-width ratio were fabricated by hydrothermal approach on a FTO substrate. The results shows that a positive response of SPV for CdS band to band transition which is correspond with the characteristics of n-type semiconductor. While the negative response in the lower energy region is correlated to sub-band-gap transitions. We utilized SPV phase for the first time to analyze the photovoltaic properties of CdS nanorod arrays and discovered the following results: The same transition processes have similar SPV phase signals, while different transition processes own their respective SPV phase signals. When the signal exhibits a break (>100°), there is a reversion of photo-generated charges direction. We can assess the band gap of a semiconductor materials by the break-point of SPV phase spectrum.2. The photo-generated charges characteristics of CdS/ZnO heterostructures materials have been studied by means of SPV techniques. The results showed that the photovoltage intensities of CdS/ZnO heterostructures materials decreased comparing with that of CdS. From the results of TPV measurement, the photo-generated electrons of CdS could transfer to ZnO under illumination since an electric field formed on the interface between CdS and ZnO. But this field is too weak to dominate the photo-generated charges characteristics. This result indicates that photo-generated charges characteristics can be clarified furthermore by means of surface photovoltage phase and transient photovoltage techniques.3. The SPV spectra of the CdS/ZnS heterostructures shows that there is a interface electric field between CdS and ZnS. It will counteract the bondage of photogenerated electrons and result in the enrichment of photogenerated holes at the surface. The SPV phase spectrum of bare CdS nanorod arrays has a break-point at 370nm, while in the case of CdS/ZnS, no obvious break-point was observed. These results show that the presence of a heterointerface will adjust the direction of the diffusion of photogenerated charges.